Method for emptying a blood circuit of an apparatus for the extracorporeal treatment of blood

ABSTRACT

A method for emptying a blood circuit of an apparatus for the extracorporeal treatment of blood after interrupting a treatment session, the apparatus comprising: a blood treatment device ( 4 ) having a fist and a second compartment ( 5, 6 ) separated from one another by a semi permeable membrane ( 7 ), an arterial pipe ( 8 ) connected to an inlet of the first compartment ( 5 ), a venous pipe ( 9 ) connected to an outlet of the first compartment ( 5 ) and a second end, a used liquid circuit ( 6, 21 ) having a drain pipe ( 21 ) connected to an outlet of the second compartment ( 6 ), whereby the method comprises the steps of: closing on itself a blood circuit ( 2 ) comprising the arterial pipe ( 8 ), the first compartment ( 5 ) of the blood treatment apparatus ( 4 ) and the venous pipe ( 9 ) in order to form a closed loop circuit, after the arterial and venous pipes ( 8, 9 ) have been disconnected from the vascular system of the patient, the blood circuit containing a liquid, transferring the liquid contained in the closed loop circuit into the used liquid circuit ( 6, 21 ), and draining the liquid transferred into the used liquid circuit ( 6, 21 ) using the drain pipe ( 21 ).

[0001] The present invention relates to a method for emptying a bloodcircuit of an apparatus for the extracorporeal treatment of blood, atthe end of a treatment session, when the blood contained in the circuithas almost been wholly returned to the patient who has undergone thetreatment.

[0002] The invention is useful in any kind of treatment in which bloodis continuously withdrawn from a patient, circulated and treated in atreatment device, and returned, once treated, to the patient.Hemodialysis, hemofiltration, apheresis and plasmapheresis are examplesof such treatment,

[0003] For the sake of clarity, the invention will be describedhereunder in relation to a specific treatment, hemodialysis, to whichhowever it is not limited as will readily appear to the persons skilledin the art.

[0004] A dialysis apparatus essentially comprises:

[0005] a filter (dialyzer) having a first and a second compartmentsseparated from one another by a semi permeable membrane;

[0006] an extracorporeal blood circuit, having an arterial pipeconnected to an inlet of the first compartment and a venous pipeconnected to an outlet of the first compartment; a blood pump isarranged on the arterial pipe and a bubble trap is connected to thevenous pipe;

[0007] a dialysis liquid circuit, having a fresh dialysis liquid supplypipe connected to an inlet of the second compartment and a used liquiddrain pipe connected to an outlet of the second compartment; a firstpump is arranged on the supply pipe and a second pump is arranged in thedrain pipe.

[0008] Each pipe of the extracorporeal blood circuit is fitted with aneedle (respectively, arterial needle and venous needle), by means ofwhich the extracorporeal circuit is connected to the patient: justbefore starting the treatment, the arterial needle and the venous needleare inserted in the fistula of the patient (portion of a vein surgicallyconnected to an artery) for respectively collecting the blood to betreated and returning the treated blood to the patient's cardiovascularsystem.

[0009] In use, the blood of the patient and the dialysis liquid arerespectively circulated in the first and the second compartments,generally in counterflow.

[0010] During a dialysis treatment, undesirable substances (by-productsof the metabolism, such as urea, creatinine, etc.) contained in theblood migrate across the semi permeable membrane from the bloodcompartment to the dialysis liquid compartment by diffusion (dialysisphenomenon, strictly speaking) and also generally by convection, afraction of plasma water being usually filtered during the treatment sothat the patient loses a few kilograms (so-called “weight loss”)corresponding to en excess of water accumulated in the body between twotreatment sessions.

[0011] At the end of a dialysis treatment, the blood pump is stopped,the arterial needle is disconnected from the fistula of the patient, andthe arterial pipe is connected to a bag containing a physiologicalsaline solution. Then the blood pump is run so that the saline solutionpushes the blood present in the blood circuit and the blood is returnedto the patient. When the cloudy interface between blood and the salinesolution reaches the venous needle, the blood pump is stopped and thearterial needle is disconnected from the fistula. Once disconnected fromthe dialysis liquid circuit, the dialyzer together with the arterial andvenous pipes are discarded in a special container for contaminated wastesince the residual blood contained in the blood circuit could becontaminated.

[0012] This way of ending a dialysis session with discarding thedialyzer connected to blood circuit full of liquid has variousdrawbacks, in particular as far as hygiene and the cost of treatment areconcerned. The venous pipe, even closed by a clamp, risks dripping andsoiling, with blood, the dialysis apparatus and the room in which theapparatus is installed and therefore contaminating the environment.Moreover since the disposal of contaminated, waste has an high cost perkilogram and the blood circuit is full of physiological saline solutionand residual blood and is therefore heavy, the cost of disposal of ablood circuit is high and represents a significant portion of theoverall cost of a dialysis treatment.

[0013] Another known method for ending a dialysis treatment consists inpumping air in the arterial pipe so as to push the blood contained inthe dialyzer and blood circuit towards the venous needle and transferthe residual blood to the patient. This method is however fairlydangerous since it entails the risk, if the transfer of the residualblood is not stopped in time, to pump air into the patient'scardiovascular system. In fact, this method is no longer used owing tothe risks for the patient.

[0014] The object of the present invention is to provide a method foremptying a blood circuit which is hygienic, safe for the patient, andless costly than the known methods.

[0015] According to the invention, a method for emptying a blood circuitof an apparatus for the extracorporeal treatment of blood, afterinterrupting a treatment session, comprises the steps of:

[0016] closing on itself a blood circuit comprising the arterial pipe,the first compartment of the blood treatment apparatus and the venouspipe in order to form a closed loop circuit, after the arterial andvenous pipes have been disconnected from the vascular system of thepatient, the blood circuit containing a liquid,

[0017] transferring the liquid contained in the closed loop circuit intothe used liquid circuit, and

[0018] draining the liquid transferred into the used liquid circuitusing the drain pipe.

[0019] According to a characteristic of the invention, the step oftransferring the liquid into the second compartment comprises the stepof causing a pressure difference across the membrane of the bloodtreatment apparatus, the pressure being higher in the first compartmentthan in the second compartment, so as to cause the filtration of theliquid through the membrane from the first compartment to the secondcompartment.

[0020] According to another characteristic of the invention, the step ofcausing a pressure difference across the membrane of the blood treatmentapparatus comprises maintaining the pressure difference slightly below apredetermined maximum pressure difference.

[0021] According to the invention, the method further comprises the stepof opening the closed loop circuit to the atmosphere when the pressurein the venous pipe reaches a predetermined low value.

[0022] This method has the advantages of reducing the weight of thecontaminated waste and of eliminating the problems caused by the liquidleaking from the blood circuit after use and contaminating theenvironment.

[0023] The invention will now be described in details. Reference will bemade to the attached drawings in which:

[0024]FIG. 1 is a schematic view of a dialysis apparatus prepared for adialysis treatment procedure and a procedure for emptying the bloodcircuit in accordance with the method forming the subject of the presentinvention;

[0025]FIG. 2 is a schematic view of the apparatus of FIG. 1 prepared fora second dialysis treatment procedure and a procedure for emptying theblood circuit in accordance with the method forming the subject of thepresent invention; and

[0026]FIG. 3 is a schematic view of the apparatus of FIG. 1 prepared fora further dialysis treatment procedure and a procedure for emptying theblood circuit in accordance with the method forming the subject of thepresent invention.

[0027]FIG. 1 represents a dialysis apparatus 1, which comprises:

[0028] a dialyzer 4 having a first and a second compartments 5, 6separated from one another by a semi permeable membrane 7,

[0029] a blood circuit 2 comprising:

[0030] an arterial pipe 8 having a first end connected to an inlet ofthe first compartment 5 and a second end fitted with a connector 11 foran arterial needle 28,

[0031] a venous pipe 9 having a first end connected to an outlet of thefirst compartment 5 and a second end fitted with a connector 12 for avenous needle 29,

[0032] a dialysis liquid circuit 3 comprising:

[0033] a fresh dialysis liquid supply pipe 20 connected to an inlet ofthe second compartment 6,

[0034] a used liquid drain pipe 21 connected to an outlet of the secondcompartment 6,

[0035] a control unit 26.

[0036] The arterial pipe 8 is fitted with a blood pump 30 forcirculating blood at a flow rate Qb and with a pressure sensor 19 formeasuring the blood pressure Pba immediately upstream of the dialyzer 4.

[0037] The venous pipe 9 is fitted with a bubble trap 10, connected to apressure sensor 17 for measuring the blood pressure Pbv downstream ofthe dialyzer 4. The bubble trap 10 is also connected to a vent 16 theopening of which is controlled by a solenoid valve 18.

[0038] The dialysis liquid supply pipe 20 is fitted with a first pump 22for circulating the dialysis liquid at a flow rate Qdi and with apressure sensor 23 for measuring the pressure Pdi immediately upstreamof the dialyzer 4.

[0039] The used liquid drain pipe 21 is fitted with a second pump 24 forcirculating the used liquid at a flow rate Qdo and with a pressuresensor 25 for measuring the pressure Pdo immediately downstream of thedialyzer 4.

[0040] The control unit 26 is connected to a user interface (notrepresented) through which it receives instructions, such as varioustarget flow rate values (blood flow rate Qb, dialysis liquid flow rateQd and, where appropriate, infusion liquid flow rate Qi, treatmentduration value T, and weight loss value WL). The control unit 26furthermore receives information output by the measuring instruments ofthe system, namely the pressure sensors 17, 19, 23 25. On the basis ofthe instructions received and the operating modes and algorithms whichhave been programmed, it controls the active components of the system,such as the pumps 22, 24, 30 and the valve 18,

[0041] According to the invention, a branch pipe 14 having a connector15 at the end thereof is connected to the arterial pipe 8 upstream ofthe blood pump 30. A plug is mounted on the connector.

[0042] During a treatment session, the dialysis apparatus of FIG. 1,operates in a conventional way; the blood circuit 2 is connected to thecardiovascular system of the patient P, the arterial needle 28 and thevenous needle 29 being inserted in the fistula of the patient P. Theblood pump 30 is running, circulating blood in the blood circuit at aflow rate Qb. The two pumps 22 and 24 arranged on the dialysis liquidcircuit 3 are running, the used liquid pump 24 running at a higher speedthan the fresh dialysis pump 25, so as to cause a difference in pressurebetween the first and second compartment 5, 6 (transmembrane pressureTMP), the pressure in the second compartment 6 of the dialyzer 4 beinglower than the pressure in the first compartment 5. As a result thereof,plasma water is filtered through the membrane 7 from the first into thesecond compartment and the programmed weight loss is achieved at the endof the treatment.

[0043] In order to end the treatment, the blood pump 30 is stopped forthe time necessary for disconnecting the arterial pipe 8 from thepatient P and for connecting it to a flexible bag 27 containing asterile saline solution (the arterial pipe 8 connected to the bag 27 isshown in broken line). Then the blood pump is run again and the bloodcontained in the blood circuit is pushed by the sterile solution towardsthe venous needle 29 and is returned to the patient P. When the cloudyinterface between the blood and the solution reaches the end of thevenous pipe 9, the blood pump 20 is stopped.

[0044] According to the invention, in order to empty the blood circuit9, which is then full of saline solution and residual blood, the venouspipe 9 is disconnected from the patient, the venous needle 29 isdiscarded and the end of the venous pipe 9 is connected to the branchpipe 14 by means of connectors 12 and 15, resulting in the blood circuit2 being closed on itself (the venous pipe 9 connected to the branch pipe14 is shown in broken line). The blood pump 30 is run again so as tocirculate the saline solution in the closed loop circuit at a moderateflow rate. The two pumps 22 and 24 arranged on the dialysis circuit arethen controlled by the control unit 26 so that the actual transmembranepressure TMP in the dialyzer 4, as calculated from the signals Pdi, Pdo,Pba, Pbv, provided by the pressure sensors 23, 25, 19 17 to the controlunit 26, is slightly below the maximum TMPmax for this type of dialyzer,which has been entered in the control unit 26 before the beginning ofthe treatment. In this operating mode, either the upstream pump 22 isstopped and only the downstream pump 24 is run, or both pumps are run atsubstantially different speeds, the speed of the downstream pump 24being faster that the speed of the upstream pump 22. As a result, theliquid contained in the closed loop is transferred, by filtrationthrough the membrane 7 from the first compartment 5 to the secondcompartment 6 of the dialyzer 4 and is then discarded through the drainpipe 21. The flexible bag 27 is rapidly emptied and deflates until itcollapses, while the pressure in the blood circuit 2 graduallydiminishes. When the signal Pbv from the venous pressure sensor 17becomes equal to a minimum. threshold value Pmin (previously entered inthe control unit 26), the control unit 26 causes the opening of thevalve 18 so as to establish communication between the closed loopcircuit and the outside and equalize the pressure inside the compartment5 with the atmospheric pressure. The blood pump 30 is run so as tocirculate the saline solution until the transfer of the solution throughthe membrane 7 is completed. Then all the pumps are stopped, the supplyand drain pipes 20, 21 are disconnected from the dialyzer 4 and thedialyzer 5, the arterial and venous pipe 8, 9 and the flexible bag 27can be discarded.

[0045]FIG. 2 represents a dialysis apparatus 1, which differs from thedialysis apparatus of FIG. 1 only in as much as it is designed tooperate with only one needle 32 instead of two needles (so-called singleneedle system). The components of this dialysis apparatus which arespecific to a single needle operation mode are:

[0046] a Y connecting pipe 31, the leg of which is connected to a needle32, and the two arms of which are fitted with a connector for respectiveconnection to the arterial pipe 8 and the venous pipe 9;

[0047] a clamp 33 arranged on the arterial pipe 8 close to the endthereof fitted with the connector 11;

[0048] a clamp 34 arranged on the venous pipe 9 close to the end thereoffitted with the connector 12;

[0049] a second blood pump 35 arranged on the venous line.

[0050] This single needle dialysis apparatus operates in a conventionalmanner, alternating blood withdrawal stages (arterial clamp 33 open,venous clamp 34 closed, arterial pump 30 running, venous pump 35stopped) and blood returning stages (arterial clamp 33 closed, venousclamp 34 open, arterial pump 30 stopped, venous pump 35 running).

[0051] When it is decided to interrupt the treatment, both blood pumps30, 35 are stopped for the time necessary for closing the arterial armof the Y connecting pipe 31 with a clamp, for disconnecting the arterialline 8 from the Y connecting pipe 31 and for connecting the arterialpipe 8 to a bag 27 containing a sterile saline solution. Then the twoblood pumps 30, 35 are run together at the same speed until the cloudyinterface between the saline solution and the blood reaches the vicinityof the end of the venous pipe 9, upon which the two blood pumps 30, 35are stopped. The venous pipe 9 is then disconnected from the Yconnecting pipe 31 and is connected to the branch pipe 14 by means ofconnectors 12, 15. The closed loop circuit is then emptied from itscontent as described above with respect to FIG. 1, both blood pumps 30,35 being run at the same speed during this final stage.

[0052] The dialysis apparatus represented in FIG. 3 is the same as thedialysis apparatus of FIG. 1, except that it further comprises means 36for infusing a sterile solution into the blood circuit 2, namely aninfusion pipe 38 connecting a container 37 for a sterile solution to thebubble trap 10 and an infusion pump 35 for circulating the sterilesolution at a flow rate Qi.

[0053] The dialysis treatment performed by the dialysis apparatus 1represented in FIG. 3 differs from the treatment described withreference to FIG. 1 in that a given quantity of infusion liquid isinfused into the cardiovascular system of the patient P.

[0054] The process for interrupting the treatment and subsequentlyemptying the blood circuit is the same as described above with respectto FIG. 1.

[0055] According to a variant not shown, the solenoid valve 18 isreplaced by a manually operated valve and, when the signal Pbv is lessthan the set value Pmin, the control unit 26 emits a visual and/oracoustic signal warning the operator that the valve must be opened.

[0056] According to a variant not shown, the blood circuit 2 comprisesan expansion chamber located between the branch pipe 14 and the arterialpipe 8.

[0057] According to a further variant not shown, the branch pipe 14 isconnected to the bag 27 and it is closed by a clasp. At the end of thedialysis treatment, the arterial pipe 8 is closed by a clamp at thevicinity of the arterial connector 11 and the arterial needle 28 isdisconnected from the fistula of the patient P. Then, the clamp isremoved from the branch pipe 14 and the saline solution contained in thebag 27 can be circulated in the blood circuit. When the cloudy mixtureof blood and saline solution reaches the vicinity of the venous needle29, the venous needle 29 is disconnected from the fistula of the patientP, is then removed from the venous pipe 9 and the connector 12 fittingthe venous pipe 9 is connected to the connector 11 fitting the arterialpipe 8 so as to close the blood circuit 2.

1. Method for emptying a blood circuit of an apparatus for theextracorporeal treatment of blood after interrupting a treatmentsession, the apparatus comprising: a blood treatment device (4) having afirst and a second compartments (5, 6) separated from one another by asemi permeable membrane (7), an arterial pipe (8) having a first endconnected to an inlet of the first compartment (5) and a second end, avenous pipe (9) having a first end connected to an outlet of the firstcompartment (5) and a second end, connection means (28, 29; 32) forconnecting the second end of the arterial pipe (8) and the second end ofthe venous pipe (9) to the vascular system of a patient, a used liquidcircuit (6, 21) having a drain pipe (21) connected to an outlet of thesecond compartment (6), the method comprising the steps of: closing onitself a blood circuit (2) comprising the arterial pipe (8), the firstcompartment (5) of the blood treatment apparatus (4) and the venous pipe(9) in order to form a closed loop circuit, after the arterial andvenous pipes (8, 9) have been disconnected from the vascular system ofthe patient, the blood circuit containing a liquid, transferring theliquid contained in the closed loop circuit into the used liquid circuit(6, 21), and draining the liquid transferred into the used liquidcircuit (6, 21) using the drain pipe (21).
 2. Method according to claim1, characterized in that the step of closing on itself the blood circuitconsists in connecting the second end of the venous pipe (9) to the endof a branch pipe (14) connected to the arterial pipe (8) the second endof the arterial pipe being further connected to a container (27) ofsaline solution.
 3. Method according to claim 1, characterized in thatthe step of closing on itself the blood circuit consists in connectingthe second end of the arterial pipe (8) to the second end of the venouspipe (9), the arterial pipe being further connected to a container (27)of saline solution.
 4. Method according to one of the claims 1 to 3,characterized in that the step of transferring the liquid into thesecond compartment (6) comprises the step of causing a pressuredifference across the membrane (7) of the blood treatment apparatus (4),the pressure being higher in the first compartment (5) than in thesecond compartment (6), so as to cause the filtration of the liquidthrough the membrane (7) from the first compartment (5) to the secondcompartment (6).
 5. Method according to claim 4, characterized in thatthe step of causing a pressure difference across the membrane (7) of theblood treatment apparatus (4) comprises maintaining the pressuredifference slightly below a predetermined maximum pressure difference(TMPmax).
 6. Method according to one of the claims 1 to 5, characterizedin that it further comprises the step of opening the closed loop circuitto the atmosphere when the pressure in the venous pipe (9) reaches apredetermined low value (Pmin).